International Publication Number 2011/028341, Gas Sparger for a Filtering Membrane, describes a gas sparger that produces an intermittent flow of bubbles even if provided with a continuous gas flow. The sparger has a housing to collect a pocket of gas and a conduit to release some of the gas from the pocket when the pocket reaches a sufficient size. A large sparger can be divided into a plurality of units each having a conduit. A gas supply pipe has at least one hole aligned with each unit to deliver air to each of the units. International Publication Number 2011/028341 is incorporated by reference.